Sweetpotato, with a global annual planting area of approximately 9 million ha, is the second most important tropical root crop. It is widely adapted, being grown in more than 110 countries. Early maturing varieties grow in 3-4 months. It is hardy and has multiple uses. Both roots and foliage are edible and provide energy and nutrients in diets. Distinct quality types have different uses, with orange-fleshed sweetpotato being valued for its extremely high provitamin A content, and other types used in varied fresh and processed forms. Sweetpotato is easily bred, as true seed is easily obtained and generation cycles are short. There are five objectives of this review. The first objective is to briefly describe recent production and utilization trends by region; the second is to review knowledge about the origin and genetic nature of sweetpotato; the third is to review selected breeding objectives. The fourth objective is to review advances in understanding of breeding methods, including: (i) generation of seed through polycross nurseries and controlled cross breeding; (ii) a description of a new accelerated breeding approach; (iii) recent efforts to systematically exploit heterosis; and (iv) new approaches of genomic selection. The fifth objective is to provide information about variety releases during the past 20 years in West, East and Southern Africa, South Asia, East and South-east Asia, China and the Pacific.

Cottonseed oil has a 2:1 ratio of polyunsaturated to saturated fatty acid. Linoleic acid is an essential fatty acid, but in large amounts it contributes to a short shelf-life due to rancidity. The aim of this study was to screen germplasm from various countries for oil and fatty acid content, to identify parents that can be used in hybridisation to increase stearic and oleic acids and reduce palmitic fatty acids. Oil content varied from 13.6% to 24.7%. Linoleic acid ranged from 51.5% to 63%, palmitic from 19.2% to 25.6%, oleic from 14.2% to 18.5% and stearic from 2.1% to 2.8%. Stearic and palmitic acids were positively correlated, and stearic and linoleic acids were negatively correlated; therefore breeding for increased stearic acid and reduced palmitic acid as well as breeding for increased stearic and linoleic acids at the same time might be difficult through conventional breeding. CIM70 and Cyto 12/74 had high values for stearic and oleic acids and Stoneville had high values of stearic and oleic acids and low palmitic acid. These can be used as parents to improve these two fractions.

In Tanzania, cotton is of great economical importance, representing a large percentage of agricultural exports, but yield and lint quality is still relatively poor. The aim of this study was to identify parents to improve boll and lint yield and quality. Parents and F1 progeny of a 7 £ 7 diallel were evaluated in four diVerent environments. Results indicated signiWcant variation for especially yield components, yield, ginning outturn and Wbre quality. Parents with high and positive GCA like NTA 93-21, Delcot 344, Auburn 56 and MZ561 and combinations with high and positive SCA for the characteristics were identiWed. Additive genetic eVects were seen for most of the characteristics, except for Wbre strength at one locality. Parents with high GCA eVects for certain characteristics produced combinations with high SCA eVects for the same characteristics. This study indicated that there is enough genetic variability for boll and lint yield and quality for eVective selection, and good parents that can be included in the breeding programme.

Fusarium wilt of cotton caused by Fusarium oxysporum f.sp. vasinfectum Atk. Sny & Hans is one of the major diseases of cotton in Tanzania. Resistant varieties provide useful tools for management of this disease. Varieties developed at Lake Zone Agricultural Research and Development Institute with previous records of resistance are currently susceptible in areas with high level of inoculums warranting the need to search for additional sources of resistance. Further, cotton varieties of Brazil indicate some level of resistance against F. oxysporum f. sp. vasinfectum that can be exploited in breeding programmes. In present study, four varieties from Brazil and three from Tanzanian were screened under greenhouse conditions for resistance to Fusarium wilt. A population of 40 plants per variety was inoculated with a crude inoculum of F. oxysporum f. sp. vasinfectum by root-dip method. Randomized complete block design was used with four replications. Resistance was evaluated on basis of foliar symptoms (disease severity index) and plant survival percentage. Further, all plants showing wilting symptoms were examined for vascular discoloration. Among various tested varieties, two cultivars from Brazil (Ipê and Aroeira) had relatively lower disease severity index and higher plant survival, these results suggesting their potential candidature for use in breeding programmes for Fusarium wilt resistance. On the other hand, two local cultivars (UK91 and UK08) presented the highest disease severity index and lowest plant survival.

Blue disease of cotton is an economically important disease of the crop first described from the Central African Republic and spread to other countries. Brazil and other South American countries record crop losses of up to 80% from infection but no cases of the disease have been reported in Tanzania.Resistance to the disease has been found in African germplasm and transferred to crop cultivars worldwide. Molecular markers linked to blue disease resistance genes have been identified presenting useful tools to identify resistant germplasm. All plants of three Tanzanian cotton cultivars (Gossypium hirsutum L.) UK91, UK08 and UKM08 showed resistance alleles for both the simple sequence repeat (SSR) (DC20027-202 bp) and single nucleotide polymorphisms (SNP) (NG0204310-C) markers but some plants of the Brazilian cultivars (G. hirsutum L.); Ipê, Cedro, Aroeira and Araça lacked resistance alleles. The findings suggest the need for caution to be taken during introduction of exotic germplasm and recognize the value of resistance trait to susceptible Brazilian germplasm when breeding for blue disease resistance.Key words: Cotton blue disease, cotton single nucleotide polymorphisms (SNPs), simple sequence repeat (SSR), resistant alleles in cotton.